A cryogenic valve with shutoff and control function has been known from, e.g., DE-OS 28 27 527.
Valves for cryogenic, i.e., extremely low-temperature media, e.g., LN.sub.2, LH.sub.2, and LHe, have generally the problem that all the seat and tappet materials are very hard at the operating temperatures of 2 K to 80 K occurring in these cases. This is equally true of metallic and nonmetallic materials. The elasticity of nonmetallic materials (e.g., Vespel), which is present at room temperature, will then disappear almost completely. This behavior makes it especially difficult to meet stringent requirements imposed in terms of tightness, which can be met, if at all, only with great design effort and development-technical efforts.
One principal problem is caused by abrasion and other particles between the sealing surfaces. However, machining-related deviations from the desired geometry are also hardly able to be compensated in the absence of elasticity.